Freewheeling diodes are used to protect power semiconductor devices against voltage spikes which occur when the power semiconductor device switches inductive loads. When suddenly disconnecting the inductive load from a current supply by turning off the active device, the magnetic energy stored in the inductive load induces a high voltage due to the sudden change of the current. A freewheeling diode provides a conductive path to carry the current driven by the inductive load which eases the current change and prevents the voltage peak caused by induction from appearing at the power semiconductor device.
Typically, pn-diodes are used as freewheeling diodes. From a perspective of reducing switching losses, Schottky-diodes provide an alternative to pn-diodes since Schottky-diodes allow for faster switching due to significantly smaller amounts of stored charge in comparison to pn-diodes.
However, the fast switching of Schottky-diodes when used as freewheeling diodes for IGBTs, for example, causes strong oscillations during switching. The oscillations lead to unwanted electronic noise. To reduce such oscillations, the switching speed, i.e. the rate di/dt with which the IGBTs are switched, can be reduced. This, however, increases the switching losses within the IGBT.
In view of the above, there is a need for improvement.